A conventional adjustable pliers generally includes two handles pivotably connected with each other by a pivot and each handle includes a jaw so that a pipe or an object can be clamped between the two jaws. The pivot includes a rectangular cross section and extends through a hole in one of the two handles and a slot in the other handle, a distal end of the pivot is connected with a nut or a C-shaped clip to prevent the pivot from being pulled out from the hole and the slot. Although the width between the two jaws can be adjusted by pivoting either of the two handles at angle, the adjustment steps are not smooth and precise enough so that the user usually tries several times to set the desired width between the two jaws.
The present invention intends to provide an adjustable device for pliers and the user simply pushes an operation member to pivot either one of the two handles till a desired width is reached, the operation member is then released to automatically set the width of the pliers.